Functions, exceptions and files

Once you can store data, the next screening topics are functions, error handling and files. Each has one idiom worth memorising.

Functions

def net_wpm(gross, errors, minutes=1):
    # Net words per minute: gross minus one word per error.
    return max(0, gross - errors / minutes)

net_wpm(45, 8)           # 37.0
net_wpm(45, 8, minutes=2)

Default arguments make a function flexible without many versions. Keep a function to one job and give it a one-line docstring; interviewers read the docstring first.

Exceptions

try:
    n = int(text)
except ValueError:
    print("Please enter a whole number")
else:
    print(n * 2)

Catch the specific exception you expect. A bare except: hides real bugs and is the thing reviewers flag most often. int("abc") raises ValueError, d["missing"] raises KeyError, [1][5] raises IndexError.

Files

with open("scores.csv", encoding="utf-8") as f:
    for line in f:
        name, wpm = line.strip().split(",")
        print(name, int(wpm))

The with block closes the file even if an error happens inside. For CSV with quotes or commas in values, use the csv module; for JSON, json.load(f) returns a dict.

A small exercise

Write a function that reads the file above and returns the name with the highest WPM. It needs a loop, a comparison, and a split. That is the shape of most take-home tasks for junior roles.